Keyboard switch construction

ABSTRACT

The disclosure describes solid-state keyboards employing a saturable magnetic core switch for each key. Each key has a keystem of magnetic material, the keystem having legs extending on opposing sides of the core. Two permanent magnets are attached to the keystem. When a key is not depressed, the magnets are located adjacent opposing sides of the core so that a flux path is formed through the core, the keystem, and the two magnets, to thereby saturate the core. When a key is depressed, the permanent magnets are moved away from the core so that it becomes unsaturated. The core is threaded by one or more wires, at least one of them being excited from an AC drive source. A switch housing of unitary construction is designed to guide the keystem, lock the switch in place in the keyboard, and hold the magnetic core in a position which facilitates threading wires through the cores.

United States Patent Victor M. Bemin Mar. 30, 1970 Oct. 12, 1971Illinois Tool Works, Inc. Chicago, Ill.

[22] Filed [45] Patented [73] Assignee [54] KEYBOARD SWITCH CONSTRUCTION11 Claims, 8 Drawing Figs.

[52] U.S. Cl 197/98, 235/145, 340/365, 337/207 [51] Int. Cl B4lj 5/08[50] Field of Search 340/365;

3,430,226 2/1969 Chow et al 340/347 3,488,613 I/l970 Marchetti 335/2073,528,535 9/1970 Bodenstein et a]. 197/107 Primary Ea'raminer Edgar S.Burr Attorneys-Robert W. Beart, Michael Kovac, Barry L. Clark and JackR. l-Ialvorsen ABSTRACT: The disclosure describes solid-state keyboardsemploying a saturable magnetic core switch for each key. Each key has akeystem of magnetic material, the keystem having legs extending onopposing sides of the core. Two permanent magnets are attached to thekeystem. When a key is not depressed, the magnets are located adjacentopposing sides of the core so that a flux path is formed through thecore, the keystem, and the two magnets, to thereby saturate the core.When a key is depressed, the pennanent magnets are moved away from thecore so that it becomes unsaturated. The core is threaded by one or morewires, at least one of them being excited from an AC drive source. Aswitch housing of unitary construction is designed to guide the keystem,lock the switch in place in the keyboard, and hold the magnetic core ina position which facilitates threading wires through the cores.

BACKGROUND OF THE INVENTION Keyboards comprise a well-known means forfeeding information into data processors. Such keyboards may take manyforms. One well-known type comprises a plurality of electrical switchcontacts mechanically operated by depressing a key. These devices suffermany disadvantages in that they are subject towear, the contacts are oroxidize and thus become unreliable, and dirt entering the keyboard mayprevent proper conduction through the switch contacts.

More recently, solid-state keyboards have been developed wherein eachkev switch comprises a permanent magnet anda core associated with a key.While these switches constitute a distinct improvement over the typeusing electrical contacts, they too suffer a number of disadvantages. Inone solid-state keyboard, the magnets associated with adjacent keys mustbe arranged such that the magnetic fields produced thereby are at rightangles so that the field from one key magnet will not afiect the coresof adjacent switches. Thus, at least two different types of switchhousings are required, and the two types are not interchangeable.

In a second type of solid-state keyboard, the magnetic cores are pottedto hold them firmly in place. This type requires a different number ofwindings and/or cores for each key, thus increasing the different typesof replacement assemblies which must be stocked. Furthermore, thepotting makes replacement difficult.

SUMMARY An object of the present invention is to provide a solid-statekeyboard switch which may readily be used in any key position on akeyboard.

An object of this invention is to provide a solid-state keyboard switchemploying a magnetic core and a housing, said housing being constructedso that it may be used at any position on a keyboard.

A further object of the invention is to provide a keyboard switchconstruction which facilitates assembly of the switch and the wiring ofa magnetic core associated with the switch.

A further object of the invention is to provide a keyboard switchhousing which fully retains all elements of the switch, and which may beeasily inserted in or removed from an opening in a keyboard supportplate.

The above-stated and other objects of the invention are accomplished byprovision of a keystem, a pair of permanent magnets, and a saturablemagnetic core. The keystem forms a generally U-shaped magnetic flux pathand the permanent magnets are attached to the legs of the keystem. Whenthe keystem is not depressed, the permanent magnets are adjacentopposite sides of the magnetic core and the core is saturated. When thekeystem is depressed, the permanent magnets move away from the core andthe corebecomes unsaturated. An AC signal source continuously applies asignal to a conductor threading the core.

The switch housing is of unitary construction and has two openingsextending therethrough from top to bottom for receiving and holding thekeystem. A first recess extends across the bottom of the housing and thefirst recess is further recessed to receive a magnetic core. Thearrangement is such that wiring in the first recess may pass through, oraround, the magnetic core. The housing includes a ledge portionextending outwardly around its upper portion for engaging the topsurface of a keyboard support plate. The housing also includes tworesilient ears which are compressed as the housing is inserted through akeyboard opening, but which expand to engage the lower surface of thekeyboard plate when the housing is fully positioned.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded view showing thenovel key switch construction;

FIG. 2 is a front view of a portion of a keyboard showing two switchesin their normal or undepressed condition;

FIG. 3 is a top view of a single switch taken along the line 3-3 of FIG.2;

FIG. 4 is a sectional side view taken along the line 4-4 of FIG. 2;

FIG. 5 is a front sectional view of the key switch housing taken alongthe line 5-5 of FIG. 3;

FIG. 6 is a perspective view of the underside of a keyboard showing howthe switch housing construction simplifies keyboard assembly;

FIG. 7 shows a modification of the switch housing; and

FIG. 8 illustrates a modified form of magnetic core for facilitatingkeyboard wiring.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 through 5 illustrate apreferred embodiment of the invention comprising a housing 10, amagnetic core 12, first and second permanent magnets 14 and 16, akeystem l8, and a keystem return spring 20. A key cap 22 is attached tothe top of the keystem.

The housing is an elongated body which may be square and need be nowider than the dimensions of the key cap. The housing may be formed ofplastic. or other nonmagnetic material and, in the disclosed embodiment,comprises an integral body formed from a single piece of polycarbonate.The housing is formed with an overhanging ledge portion 10a extendingpartially around its top. A portion of two opposing sides of the housingare formed at an angle to the length of the housing so as to provide twoears 10b. The cars 10b have a certain degree of resiliency so that theyare compressed slightly as the switch housing is inserted downwardlythrough a hole in a keyboard support plate 24 as shown in FIG. 2. Afierthe ears pass through the hole they expand outwardly to prevent upwardmovement of the housing. The ledge 10a prevents downward movement. Thus,the housing may be firmly locked in position in the keyboard plate. Ifnecessary, the housing may be removed from the plate by pressing theears inwardly and lifting the housing.

The housing has a longitudinal opening 27 extending downwardlytherethrough for receiving the keystem 18 which, as shown in F IG. 1, isa generally boxlike structure having two legs 18a and 18b. A centralportion 10c of the housing extends from one side of the housing to theother, thus bisecting the lower portion of the opening 27 as shown inFIGS. 3-5. A post 10d extends upwardly from central portion 10c toretain a compression spring which is compressed between portion 10c ofthe housing and the underside of the top portion of the keystem.

The keystem has a portion of one side 18d (FIG. 4) removed so that legs18a and 18b may straddle the central portion 10c of the housing. Side184 of the keystem is formed with two downwardly extending ears 18c asshown in FIG. 1. After the keystem is inserted through the opening inhousing 10, the ears are bent outwardly. When so bent, the ears engagethe lower edges of the housing 10 and limit upward movement of thekeystem in response to the bias exerted on the keystem by thecompression spring 20.

The central portion 10c the housing is formed so as to have a recess 10:in its bottom surface that extends across it between opposing sides. Afurther recess 10] (FIG. 5) is formed perpendicular to recess l0e andextending through the central portion 10c of the housing. A ferritetoroidal core 12 is positioned in the further recess so that its centeropening is aligned with recess 102. As shown in FIG. 4, this arrangementlocates the core 12 so that it may be readily threaded by one or morewindings 26 and 28, the walls of recess l0e serving as guiding surfacesfor the windings as they approach the core opening during the threadingoperation. The core may be force fit into the recess or else held inplace by a suitable adhesive material. The core may be made from ferriteor material exhibiting low magnetic remanence properties.

As shown in FIG. 4, the central portion of the housing has twodownwardly depending legs 10h. An opening 10g (FIGS. 5 and 6) is formedthrough each of these legs, the openings being aligned with the recessf. As shown by the dotted outline of core 12 in FIG. 4, the core extendsinto these openings almost to the side surfaces of central portion 10cagainst which the magnets 14 and 16 may slide. This arrangement permitsthe core 12 to be positively positioned in close proximity to magnets 14and 16 when the keystem is not depressed.

The legs 18a and 18b of the keystem are punched and bent inwardly toform four tangs 18c. These tangs engage recesses in permanent magnets 14and 16 to hold the permanent magnets for movement with the keystem. Byway of example only, the keystem may be formed from nickel-plated steeland the pennanent magnets from a barium ferrite filled compound. Themagnets 14 and 16 are attached to legs 18a and 18b so that the southpole of one magnet and the north pole of the other is adjacent themagnet core. Furthermore, as illustrated in FIG. 4, the magnets aremounted on the keystem so as to be directly opposite and closelyadjacent core 12 when the key 12 is in its normal or undepressed state.Preferably, the outer diameter of core 12 is slightly less than thewidth of the central portion 10c of the housing so that the permanentmagnets do not touch the core as they slide along the sides of theportion 100.

The electrical and electromagnetic aspects of the switch are disclosedin my copending application Ser. No. 879,220, filed on Nov. 24, 1969, towhich reference may be made for a detailed description of its operation.Briefly, when the switch is in the normal or undepressed state as shownin FIG. 4, the permanent magnets are directly opposite and closelyadjacent the core 12. A flux path is established from the north pole ofmagnet 14 through the keystem 18, through magnet 16, and throughparallel paths in core 12, back to the south pole of magnet 14. Sincethe flux takes the path of least resistance, flux in the gap between themagnets will concentrate in the core, thereby causing saturation.

When the switch is in the depressed state, the permanent magnets aremoved away from core 12 and the core desaturates. The core may be usedas a transformer or a variable inductor in switching circuits.Furthermore, a plurality of switches may be used in a keyboard toprovide a coded or a noncoded output as described in the aforementionedcopending application.

FIG. 6 is a perspective view of the underside of a keyboard and, inconjunction with FIGS. 2 and 5, illustrates some of the advantages ofthe novel switch construction when a plurality of switches are used in akeyboard. As shown in FIG. 2, each switch housing requires nomorekeyboard space than that required for the key cap 22, the key capbeing of a size normally used in typewriter and other keyboards. Thus,as shown in FIG. 6, the switch housings may be closely positionedadjacent each other without the magnetic fields from one switchinfluencing the operation of any other switch.

In most keyboard applications it is anticipated that the switch housings10 will be inserted through openings 29 in the keyboard support plate 24so that the recesses 10c are aligned for each row of keys. Asillustrated in FIGS. 2 and 6, this will place the holes in cores 12 foreach row of switches in axial alignment. This'simplifies the process ofinserting the core windings if the wiring is done after the cores areattached to the housing 10.

The novel switch construction also permits threading of the cores beforethe cores are attached to the housing 10. In this case, the cores aremounted in an automatic wiring jig of a type well known in the art andautomatically threaded in either a coded or a noncoded fashion. As asimple illustration, an input winding 26 (FIG. 2) may be threadedthrough the cores for all keyboard switches whereas one or more windings28 are selectively threaded through the cores. FIG. 2 illustrates onewinding 28 threaded through the core 12 of one switch and threadedaround the core 12' of a second switch. Coding is more fully explainedin the copending application referenced above.

After the cores are threaded, they and their windings are removed fromthe wiring jig and laid out in a pattern as illustrated in FIG. 6. Theindividual cores are inserted through openings 10g into recesses 10f andattached to the housings 10 by an adhesive, by staking, or by some othersuitable means.

From the foregoing description, it is obvious that the novel switchconstruction facilitates keyboard assembly and requires no specialconsideration to meet customer demand. If a customer desires a keyboardwith a staggered key arrangement rather than having keys aligned inrows, all that is required is a support plate 24 with the holes 29fonned in staggered arrangement. No changes are required in theindividual switches, their wiring or method of assembly.

If a customer desires a keyboard comprising an alphabetic oralphanumeric section and a numeric section, two keyboard sections mayutilize a common support plate 24 or may, in effect, comprise twoseparate keyboards located on separate plates. The wiring of thekeyboard remains essentially the same.

The novel switch may be used in noncoded keyboards or in keyboardsproducing a coded output in any code desired by the customer. Theconstruction of the switch remains the same and only the core threadingoperation need be varied to obtain the desired code.

It should be noted that the present invention permits use of permanentmagnets having dimensions 1 and w such that the ratio of l/w is quitesmall. For lower ratios of l/w the rate of change of flux in the airgapbetween magnets is higher thus requiring smaller keystem movement inorder to accomplish the switching function. For lower ratios of l/w, themaximum flux density is lower but is still sufficient to saturate thecore.

FIG. 7 shows a modified form of switch housing construction wherein afurther recess 30 extends upwardly from the top of recess 10c, therecess 30 extending from one side of the housing 10 through to theopposing side. This arrangement permits some or all of the windingswhich do not pass through a core to be firmly held in position. Thewindings may be threaded through recess 30 after core 12 is attached tothe housing, or they may be bundled together and inserted upwardly intorecess 10e so as to be loosely trapped in recess 30 when the core isattached to the housing.

FIG. 8 illustrates another method of switch construction wherein thecore 12 has an airgap 32 through which wires may be passed edgewise tothe central opening of the core. After the desired windings are insertedthrough the airgap, it may be closed to retain the windings.

While preferred embodiments of the invention have been shown anddescribed, it will be understood that various substitutions andmodifications may be made without departing from the spirit and scope ofthe invention as defined by the appended claims.

Iclaim:

1. In a solid-state switch of the type wherein first and second magnetscarried on first and second legs of a keystem are moved into and out ofsaturable position with respect to a magnetic core of a type having oneor more windings extending through a center opening, the improvementcomprising:

a switch housing having a longitudinal opening extending therethroughfor receiving and guiding said keystem;

said switch housing having a central portion extending from one side ofthe housing to an opposing side;

said central portion having a first recess in its bottom surface,forming an unobstructed path from said one side to said opposing side;

said central portion having a second recess transverse to said firstrecess and extending upwardly therefrom for receiving said magneticcore;

said second recess having a depth relative to said first recess wherebythe center opening in said core is aligned with the uppermost surface ofsaid first recess when said core is positioned in said second recess;

the center opening of said core having a curvature over a portionthereof which is the same as the curvature of the uppermost surface ofsaid first recess, whereby said uppermost surface may serve as a guidefor threading a winding through said center opening.

2. The improvement as claimed in claim I wherein said core is a toroidalcore and said uppermost surface of said first recess is semicircularwhereby the inner surface of said core and said uppermost surface arealigned over approximately 180.

3. The improvement as claimed in claim 1 wherein the width of said coreis slightly less than the width of said central portion of said housing,said second recess extending entirely entirely across the width of saidcentral position whereby said core'may be inserted into said secondrecess from the bottom of said central portion and any wires threadedthrough said core are retained by the core so as to lay in said firstrecess.-

4. The improvement as claimed in claim 1 wherein said housing includesledge portions extending outwardly from the sides thereof at the top ofsaid housing, said housing including two resilient ears extendingoutwardly and upwardly from opposing sides thereof toward said ledge.

5. The improvement as claimed in claim 1 wherein said first recess has athird recess in the upper surface thereof, said third recess beingparallel to said first recess and deeper than said second recess wherebywindings not threading through said core may bypass said core by beingthreaded through said third recess.

6. The improvement as claimed in claim 1 wherein said core has an airgapthrough which windings may be edgewise inserted to thread said core.

7. The improvement as claimed in claim 1 wherein said housing includingsaid central portion is a plastic piece of unitary construction.

8. A keyboard comprising:

a support plate having at least one row of openings therein;

a switch housing extending through each of said openings,

each said housing having a longitudinal opening extending therethrough,and,

a central portion extending from one side of the housing to an oppositeside inside said housing to divide said longitudinal opening into firstand second openings;

said central portion having a first recess in its bottom surface fonningan unobstructed path from said one side to said opposite side;

a magnetic core having a center opening therein for each said housing;

said central portion of each housing having a second recess transverseto said first recess and extending upwardly therefrom for receiving oneof said magnetic cores;

said second recess having a depth relative to said first recess wherebythe center opening in said core is aligned with the uppermost surface ofsaid first recess when a core is positioned in said second recess;

the center opening of each core having a curvature over a portionthereof which is the same as the curvature of the uppermost surface ofsaid first recess;

said housings for one row being positioned whereby said first recessestherein are aligned to form an unobstructed straight line path throughthe center openings of all cores in said one row.

9. A keyboard as claimed in claim 8 wherein:

the width of each core is slightly less than the width of the centralportion of each housing; and

said second recess extends entirely across the width of said centralportion whereby each core may be inserted into said second recess fromthe bottom of said central portion;

said keyboard further comprising a plurality of windings extending alongsaid aligned first recesses and selectively threading said cores.

10. A keyboard as claimed in claim 9 wherein each said housing has anoutwardly extending ledge portion for engaging said support plate tothereby limit downward movement of the housing, each said housingincluding resilient outwardly and upwardly extending ears that arecompressed as the housing is inserted through a hole in the supportplate but expand to engage and lower side of said support plate oncethey have passed throu h the hole.

l A key oard as claimed in claim 9 and further comprising:

a keystem and first and second magnets for each housing;

each keystem including opposing parallel legs interconnected by agenerally U-shaped member;

each keystem being inserted into the longitudinal opening through ahousing whereby said parallel legs are on opposing sides of said centralportion and said U-shaped member straddles said central portion;

one of said magnets being mounted on each said leg between said leg andsaid central portion.

1. In a solid-state switch of the type wherein first and second magnetscarried on first and second legs of a keystem are moved into and out ofsaturable position with respect to a magnetic core of a type having oneor more windings extending through a center opening, the improvementcomprising: a switch housing having a longitudinal opening extendingtherethrough for receiving and guiding said keystem; said switch housinghaving a central portion extending from one side of the housing to anopposing side; said central portion having a first recess in its bottomsurface, forming an unobstructed path from said one side to saidopposing side; said central portion having a second recess transverse tosaid first recess and extending upwardly therefrom for receiving saidmagnetic core; said second recess having a depth relative to said firstrecess whereby the center opening in said core is aligned with theuppermost surface of said first recess when said core is positioned insaid second recess; the center opening of said core having a curvatureover a portion thereof which is the same as the curvature of theuppermost surface of said first recess, whereby said uppermost surfacemay serve as a guide for threading a winding through said centeropening.
 2. The improvement as claimed in claim 1 wherein said core is atoroidal core and said uppermost surface of said first recess issemicircular whereby the inner surface of said core and said uppermostsurface are aligned over approximately 180*.
 3. The improvement asclaimed in claim 1 wherein the width of said core is slightly less thanthe width of said central portion of said housing, said second recessextending entirely entirely across the width of said central positionwhereby said core may be inserted into said second recess from thebottom of said central portion and any wires threaded through said coreare retained by the core so as to lay in said first recess.
 4. Theimprovement as claimed in claim 1 wherein said housing includes ledgeportions extending outwardly from the sides thereof at the top of saidhousing, said housing including two resilient ears extending outwardlyand upwardly from opposing sides thereof toward said ledge.
 5. Theimprovement as claimed in claim 1 wherein said first recess has a thirdrecess in the upper surface thereof, said third recess being parallel tosaid first recess and deeper than said second recess whereby windingsnot threading through said core may bypass said core by being threadedthrough said third recess.
 6. The improvement as claimed in claim 1wherein said core has an airgap through which windings may be edgewiseinserted to thread said core.
 7. The improvement as claimed in claim 1wherein said housing including said central portion is a plastic pieceof unitary construction.
 8. A keyboard comprising: a support platehaving at least one row of openings therein; a switch housing extendingthrough each of said openings, each said housing having a longitudinalopening extending therethrough, and, a central portion extending fromone side of the housing to an opposite side inside said housing todivide said longitudinal opening into first and second openings; saidcentral portion having A first recess in its bottom surface forming anunobstructed path from said one side to said opposite side; a magneticcore having a center opening therein for each said housing; said centralportion of each housing having a second recess transverse to said firstrecess and extending upwardly therefrom for receiving one of saidmagnetic cores; said second recess having a depth relative to said firstrecess whereby the center opening in said core is aligned with theuppermost surface of said first recess when a core is positioned in saidsecond recess; the center opening of each core having a curvature over aportion thereof which is the same as the curvature of the uppermostsurface of said first recess; said housings for one row being positionedwhereby said first recesses therein are aligned to form an unobstructedstraight line path through the center openings of all cores in said onerow.
 9. A keyboard as claimed in claim 8 wherein: the width of each coreis slightly less than the width of the central portion of each housing;and said second recess extends entirely across the width of said centralportion whereby each core may be inserted into said second recess fromthe bottom of said central portion; said keyboard further comprising aplurality of windings extending along said aligned first recesses andselectively threading said cores.
 10. A keyboard as claimed in claim 9wherein each said housing has an outwardly extending ledge portion forengaging said support plate to thereby limit downward movement of thehousing, each said housing including resilient outwardly and upwardlyextending ears that are compressed as the housing is inserted through ahole in the support plate but expand to engage and lower side of saidsupport plate once they have passed through the hole.
 11. A keyboard asclaimed in claim 9 and further comprising: a keystem and first andsecond magnets for each housing; each keystem including opposingparallel legs interconnected by a generally U-shaped member; eachkeystem being inserted into the longitudinal opening through a housingwhereby said parallel legs are on opposing sides of said central portionand said U-shaped member straddles said central portion; one of saidmagnets being mounted on each said leg between said leg and said centralportion.